Removable subsea drilling guide arm base



R. P. THOMAS REMOVABLE SUBSEA DRILLING GUIDE ARM BASE Sept. 2, 1969 Filed Dec. 12, 1967 2 Sheets-Sheet 1 INVENTOR ROY P. THOMAS BY ,0

M0 M ATTORNEY Sept. 2, 1969 R. P. THOMAS I REMOVABLE SUBSEA DRILLING GUIDE ARM BASE 2 Sheets-Sheet 2 Filed Dec. 12, 1967 INVENTOR. ROY P. THOMAS M ATTORNEY United States Patent 3 464 48 REMOVABLE SUlivSEA DRILLING GUIDE ARM BASE US. Cl. 166-.5 4 Claims ABSTRACT OF THE DISCLOSURE In drilling oil and gas wells or the like from a floating vessel in a marine location, it is ordinarily convenient to employ in the early stages of the drilling a set of guide cables, or lines, connecting the drilling vessel or floating platform with the top of the well, so that the drilling equipment may be lowered in such a way that it will index, or be located accurately to re-enter the well. In order to do this the drilling base (a very heavy plate-like member with a substantially central hole) is initially locked on the sea bottom. It frequently includes surface casing, or surface casing is very early placed through this drilling base and cemented in place, all is well known in this art. On this drilling base a guide arm base is then fastened, thus establishing the location of the guide cables for the subsequent manipulations of the drilling equipment.

It is desirable to remove the guide arm base. This invention utilizes a removable guide arm base which is easily attached initially to the surface casing or an equivalent projection from the drilling base. It is of adequate strength for all functional operations and at the time that the blowout preventers are removed, this guide arm base can be unlatched and retrieved. It may also be re-installed on temporarily abandoned marine well heads.

Background of the invention Marine drilling from a floating platform or vessel has been carried on for a number of years. Techniques for manipulating the drilling equipment through a conductor pipe of adjustable orientation and dimensions have become well known. In the early stages of such drilling it has been found convenient to employ guide cables, or lines, extending from the drilling 'base on the sea floor up to the floating platform or vessel. By suitable yokes sliding on these guide lines, it is possible to orient the lower end of a drill string, casing, drilling apparatus such as a blowout preventer stack, etc., to the opening in the drilling base, customarily defined by the top of the surface casing. Such an orientation system is shown, for example in US. Patent 3,177,954 issued to W. W. Rand, as well as in the brochure Cameron Marine Systems issued by the Cameron Iron Works, Inc., in 1966, and in other publications. This invention particularly deals with the guide arm base, which is provided immediately above the drilling base and ordinarily attached to the projecting surface casing. This guide arm base is utilized to fix the lower end of the guide lines and, therefore, assists in guiding the riser, the blowout preventer stack, and other equipment which is latched onto the surface casing, or at least anchored with respect to it.

Ultimately it is desirable to remove this guide arm base for two reasons. First, the base may be reused, resulting in a tangible saving in equipment costs. Second, the removal of this base leaves the upper part of the well clear of obstructions which might otherwise hamper the installation of a platform or the like over the well for tieback at a future date. However, this introduces the difiiculties that such a removable guide arm base must be capable of quite firm and strong attachment to its support which defines the top of the well and must subsequently be capable of unlatching after an indeterminate period of use in the marine environment. In other words, the latching and unlatching must be quite definite and positive, regardless of the intervening period. In the latched state, the guide arm base must withstand varying stresses which are changing all the time. Furthermore, there can be essentially no .play with respect to the well head or wear will occur which will ultimately destroy the function of this equipment. When the base is unlatched, it must be capable of vertical removal without fouling the well or well head.

Nonremovable guide arm bases have been customarily used in the past and are described in a series of US. patents, for example Bauer et al., 2,808,229, J. E. Lacy 3,080,921, W. W. Rand 3,177,954, etc., and are also shown in engineering publications such as the Cameron brochure mentioned above. Recently a type of removable guide arm base has been employed which corresponds to the US. patent 3,321,015 Word, but difliculties are encountered. Essentially such a base is made up of two mating halves hinged together. Hinge pin failure has been experienced, resulting in bent guide arms. A hydraulically actuated latch is employed which is both expensive and of doubtful certainty of operation after long exposure on the marine floor. Finally, the guide posts (which anchor the guide cables) prevent use of a continuously threaded cable system revealed later in this disclosure.

Summary of the invention This invention comprises a removable guide arm base including a hollow cylindrical member slightly larger than the surface casing and longer than its outer diameter, to the upper part of which is attached a number (ordinarily 4) of guide arms extending radially outward and of approximately equal length, which are braced by diagonal braces attached (for example by welding) to the lowest part of the central cylinder. Near the outer end of each guide arm there is an anchor for a guide line. On the inner part of the guide arm and adjacent the cylindrical member there is a latch so arranged that the latch can detachably engage the casing. This latch is movable between locking and unlocking positions. In the former it engages the surface casing, or its equivalent, and thereby transmits vertical pull from the drilling vessel, or the like, to the formations beneath the sea; whereas, in the unlatched position it can be removed by using the guide lines as a hoist, provided that any equipment latched to the surface casing above this point and of greater diameter has been at least temporarily removed. This latching means is adapted to be actuated from the location of the guide arm base although it can also be arranged for actuation from the drilling vessel if desired.

Brief description of the drawings FIGURE 1 shows in diagrammatic form a side view of a marine drilling apparatus with the removable guide arm base latched to the surface casing.

FIGURE 2 is a side view, partly in elevation and partly in section.

FIGURE 3 shows a detail of the surface casing, including a preferred form of indexing arrangement for the removable guide arm base.

FIGURE 4 is a plan view of a guide arm base similar to that shown in FIGURE 2.

Description of the preferred embodiment Referring now to FIGURE 1 a floating platform, or supporting structure such as a boat, part of which is shown at 10, is anchored by means (not shown) above the earth 11 and below a body of water 12. Since the manipulations carried out on the floating platform do not constitute a part of this invention, they will be described only generally. Such operations are, of course, very well known by now. A conductor pipe, or surface casing 13, is made up on the platform of any suitable length. At one end it is provided with a locking ring, for example a Y slot section 14 (shown in more detail in FIGURE 2). Below this are Welded a plurality of ribs 15 proiecting radially outward. A removable gmide arm base, indicated generally by 16, can then be slipped over the Y slot section 14.

This removable guide arm base includes as basic structure a hollow cylindrical member 17 which is slightly larger in inner diameter than the maximum dimension of the casing 13, for example of the order of 1 inch to A inch greater diameter than the outside diameter of the Y slot section 14. Attached to this cylindrical member, for example by welding, are a plurality of guide arms 18 extending substantially radially outward. These are of approximately horizontal and of equal length, and each is attached to the upper part of the cylindrical member 17. For further bracing, diagonal members 19 are attached, preferably by welding, to the outer part of the guide arms 18 and the lower part of the cylindrical member 17. Preferably, though not essentially, the cylindrical member 17 is provided at its lower extremity with a skirt 20, flared somewhat, and provided with notches 21 suitable for engaging the upper portion of the ribs 15. This skirt is provided so the guide arm base assembly 16 can be guided back over a subsea well head (such as the Y slot section 14) after the well has been abandoned and it has been decided to re-enter it for any reason.

It is apparent that the notches 21 are provided in skirt 2%) to receive ribs 15 so that the guide arm base assembly 16 when lowered to the position shown cannot be rotated with respect to the casing 13. Also, the ribs 15 provide a foundation for landing the guide arm base assembly 16 should it be necessary to rerun this assembly over an abandoned well head, as discussed above.

Ordinarily bracing is provided between the radially extending guide arms, not only against vertical pull but against horizontal stresses. A simple but satisfactory method of accomplishing this involves attaching, for example by welding, a cross brace 22 between outward extremities of adjacent arms 18.

When the removable guide arm base 16 has been slipped down over the Y slot section 14 until ribs 15 engage the skirt 20, the base must be locked into place securely. One system for accomplishing this is shown, for example in FIGURE 2. Here the Y slot section contains a groove 23 and a series of locking devices 24, or dogs, each slidably mounted on a radial arm 18 and provided with a latching extension so that when the latching means 24 is in locked position (as shown in FIGURES 2 and 4) the outer end of latching extension 25 engages groove 23. The thickness of latching extension 25 is only slightly less than that of groove 23 and the outer part of latching means 24 closely conforms to the cross section of the arm 18 so that there is little play in these parts and, accordingly, the removable guide arm base 16 is effectively locked against the casing 13. I prefer that this mechanical play he not greater than for example inch.

The latching means 24 is furnished with a positive lock which will prevent radial motion of this member with re spect to arm 18. One example of such a lock is shown in FIGURES 2 and 4, consisting of headed pins 26 which are aligned and passed through vertical holes (such as holes 27) in the arm 18 when the latch is in the unlocked position and similar holes (unnumbered) when the latching means is in the locked position shown. Such pins 26 would normally be provided with means (not shown) such as link chain or the like, for holding them to the arm 18, but still permitting them to be withdrawn from the latching means so that it may be moved. Preferably the pins 26 fit snugly through the corresponding latches 24 and arms 18 so that when the latches are in engaged position, ordinary vibration or the like cannot possibly cause the pins to leave the holes and permit the latches to disengage.

With the apparatus thus far discussed locked in place, and the surface casing 13 attached to the drilling base 28 (which, for the purposes of this invention can be described as simply being a large heavy disc-shaped mass located in some way to the casing 13), the assembly is then oriented vertically and either jetted into place, lowered into place if a suitable hole has already been drilled in the ocean floor, or driven into place until the large mass of the drilling base 28 is firmly in position on the ocean floor. The surface casing 13 may then be cemented in place.

The removable guide arm base must, of course, contain means near the outer end of each of the guide arms 18 for anchoring a guide line and thus sustaining it against vertical pull. Many such devices are known. One that I prefer includes a plurality of sheaves 29 mounted with horizontal axis at the outer extremities of the guide arms 18. These are grooved to accept a multiple-strand steel cable 30 (shown only in FIGURE 1), which extends up to the floating platform 10 and which is maintained in tension at all times. If this sheave system is employed, the cable extends downward from the floating vessel, through two adjacent sheaves, and back up to the floating vessel again, so that both ends of the cable are continuously available and so that the cable may be withdrawn without fouling if a cable break occurs. Suitable means, shown diagrammatically in FIGURE 1 as further sheaves 31 and a weight 32 are mounted on the floating platform 10 to supply constant tension to the cables 30. Other types of constant tensioning devices, such as torque motor can be used instead of the elementary system shown and, if desired, one end of the cable may be atfixed to the vessel (as at 71) and constant tension applied to the opposite end.

With such a set of guide cables it is, of course, easy to send down with a yoke (such as yoke 33) a set of well head components, such as a blowout preventer stack indicated generally at 34, and a marine riser pipe 35 coupled to the well head components, through a flex joint generally indicated at 36. The upper part of the marine riser pipe 35 would also include a slip joint 37 supported from the rig 38 mounted on the floating platform 10 or some other part of the floating platform 10. The rig 38 supports the riser pipe assembly and well head components as they are lowered down and indexed by the yoke 33 cooperating with the guide lines 30 so that latching ultimately takes place between the bottom of this assembly and the top of the casing 13 (by means not shown but well known in this art).

Ultimately it is desired, when the drilling is complete, to remove the guide arm base, for reasons discussed earlier. By this point the riser pipe 35 and the well head components 34 have been removed.

To remove the guide arm base it is now necessary to remove the pins 26 and slide back the locking means 24. One system for accomplishing this, using the apparatus shown in the drawings, is by means of a diver. This also permits the diver to remove any marine growth found on an arm 18. However, this is not the only means of accomplishing this. Pyrotechnic devices are well known, such as explosive bolts and the like. It is possible to blow oif the front section 25 of the latching means 24 without the use of a diver, in case the well is being drilled in water so deep that the use of a diver is hazardous. It is possible, though normally undesirable, to arrange other remote control means, such as a hydraulically actuated latch of the type shown in the Cameron brochure referred to, or the Rand patent listed above. In other words, the presence of this positive latching means on the guide arms is essential but the type may vary, depending upon the particular user, so long as the latching means is slidably disposed on the guide arm so that it may be moved laterally between engaging and disengaging positions, and

particularly if a means is provided for positively locking the latch in either of these two positions.

It is apparent that variations may be made in this fundamental design without departing from the spirit of the invention. In general, the invention discussed herein is best defined by the appended claims.

I claim:

1. In marine drilling equipment including a casing containing a groove or equivalent, a removable guide arm base comprising a unitary hollow cylindrical member slightly larger in inner diameter than said casing and longer than its outer diameter,

a plurality of substantially radially extending guide arms of at least approximately equal length, each attached to the upper part of said cylindrical member and diagonally braced against the lower part of said cylindrical member,

means near the outer end of each of said guide arms for anchoring a guide line against vertical pull on said line, and

latching means disposed on said guide arms adjacent said cylindrical member for detachably engaging said groove in said casing, whereby said guide arm base can be pulled up away from said casing when said latching means is disengaged.

2. Apparatus in accordance with claim 1 in which separate latching means is provided on each of said guide arms.

3. Apparatus in accordance with claim 2 in which each of said latching means is slidably disposed on its guide arm so that it can be moved laterally between engaging and disengaging positions.

4. Apparatus in accordance with claim 3 in which each of said latching means is provided with a positive lock for maintaining said latch in engaged or disengaged positions.

References Cited UNITED STATES PATENTS 3,220,477 11/1965 Jones 166.5 3,259,191 7/1966 McClintock et a1. 166--.5 X 3,302,709 2/ 1967 Postlewaite 166-.6 3,321,015 5/1967 Word 166-.5 3,341,398 9/1967 Nicolson --7 CHARLES E. OCONNELL, Primary Examiner R. E. FAVREAU, Assistant Examiner U.S. Cl. X.R. 175-7 

